Auxiliary lighting system for a gaseous discharge lamp

ABSTRACT

An emergency or auxiliary lighting system for a gaseous discharge lamp is provided with an auxiliary lamp controlled by a switch which is biased to remain in a closed position. A control circuit, responsive to the voltage across the gaseous discharge lamp, produces a voltage proportional thereto which is opposed to the biasing control. During any time that the gaseous discharge lamp provides more than a minimum adequate light output, the control circuit voltage becomes greater than the biasing control to open the switch. Also, in the event of a power interruption, the control circuit closes the switch.

United States Patent Gershen AUXILIARY LIGHTING SYSTEM FOR A GASEOUSDISCHARGE LAMP Bernard J. Gershen, Centerport, N.Y.

Assignee: Leviton Manufacturing Co., Inc.,

Little Neck, NY.

Filed: Oct. 5, 1973 Appl. N0.: 403,948

Inventor:

u.s. c1 315/92, 315/91, 315/120, 315/135 1m. (:1. H05b 41/46, H05b 37/04Field of Search 315/88, 91, 92, 119, 120, 315/121,127,129,130,131,135,178,182

3,783,332 l/1974 Peterson ct al. 3l5/9l Primary ExaminerR. V. RolinecAssistant Examiner-E. R. LaRoche Attorney, Agent, or Firm-Hanse l-l.Hamilton [57] ABSTRACT An emergency or auxiliary lighting system for agaseous discharge lamp is provided with an auxiliary lamp controlled bya switch which is biased to remain in a closed position. A controlcircuit, responsive to the voltage across the gaseous discharge lamp,produces a voltage proportional thereto which is opposed to the biasingcontrol. During any time that the gaseous discharge lamp provides morethan a minimum adequate light output, the control circuit voltagebecomes greater than the biasing control to open the switch. Also, inthe event of a power interruption, the control circuit closes theswitch.

6 Claims, 4 Drawing Figures AUXILIARY LIGHTING SYSTEM FOR A GASEOUSDISCHARGE LAMP BACKGROUND OF THE INVENTION This invention relates toanemergency lighting system, and more particularly to an auxiliarylighting circuit for use with a primary lighting system.

Gaseous discharge lamps, such as mercury arc lamps, metal are lamps andsimilar type lamps, have long been used in industrial lightingfacilities as well as on highways because of their extremely highefficiency when compared to other sources of light. This type of lamphas the property of requiring a relatively high voltage for striking thearc to light the lamp, and requires a relatively lower voltage formaintaining the arc. These requirements are handled by various types ofballasts which are commercially available.

One of the problems in using such gaseous discharge lamps resides in thefact that, upon interruption of power for a few cycles, the lamp willbecome extinguished andrestriking of the are within the lamp will notoccur immediately upon restoration of the power source. One reason forthis is that the striking potential of a hot lamp is much higher thanthe striking potential when the lamp is cool. Thus, when the gaseousdischarge lamp is initially turned on while in a cool state, the ballastwill provide sufficient voltage to strike an arc in the lamp. After thelamp has been operating for a length of time, it heats up and should apower interruption occur, a return of power to the line of the hot lampwill require a greater striking potential than the ballast is capable ofproviding. The lamp will therefore not immediately strike and mayrequire as much as fifteen minutes to cool sufficiently before theballast voltage will restrike the are. If this should occur in a factoryor office, a safety hazard may very well result. Similarly, when used inhighwaysthe absence of sufficient lighting for a length of time maycontribute to the occurrence of accidents or other resultingemergencies.

An additional problem which occurs when using gaseous dischargelampsresides in the fact that once the arc is struck there is an initialwarmup of the gaseous discharge until the potential across the lampprovides adequate lighting output.

To facilitate the use of gaseous discharge lamps it is desirable toprovide an emergency or auxiliary lighting circuit in conjunction withthe gaseous discharge lamp to provide illumination during the off andwarm-up periods ofthe lamp. While various circuits have been suggestedin the past for providing such emergency illumination, such circuitshave in general been relatively complicated, expensive, inefficient, andhave employed many components.

Many of the circuits available in the prior art only provide auxiliarylighting which will solve the first of the aforementioned problems.Namely, the auxiliary lighting circuits will be only turned on after apower interruption while the gaseous discharge lamp is cooling offawaiting restriking by the ballast output voltage. However, these priorart circuits will turn off as soon as the gaseous discharge lamp hasbeen restruck. Therefore, during the period of time that the gaseousdischarge lamp has not reached sufficient illumination to provide normaldesired lighting output, the auxiliary circuit will not provide anyassistance to compensate for such lack of proper illumination.

Other known devices do provide auxiliary lighting which will respond toboth aforementioned problems. Namely, in addition to the auxiliarylighting being turned on following a power interruption, this auxiliarylighting will also remain on during the warm-up period until the gaseousdischarge lamp reaches the normal desired illumination output level.However, most of these circuits make use of relays involving a relaycoil in series or in parallel with the ballast output. This requiresstringent manufacturing restrictions on the design of the relay coilsuch that it will not have an adverse effect on the gaseous dischargelamp wattage. Furthermore, the use of relay coils necessarily involvesan electromechanical device which is not always reliable. In addition,these prior art circuits generally require two switching devices whereinoneof the switching devices controls the turning on of the auxiliarylighting during the initial warm-up period, while the second switchingdevice serves to disconnect the first switching device during powerinterruption such that the auxiliary lighting will remain turned on.

SUMMARY OF THE INVENTION It is therefore an object of the presentinvention to provide a novel emergency or auxiliary lighting system forgaseous discharge lamps which avoids the aforementioned problems of theprior art devices.

Another object of the invention is to provide an emergency lightingcircuit for gaseous discharge lamps which does not contain relayswitches.

Yet another object of the invention is to provide an emergency lightingsystem for gaseous discharge lamps which uses a single switching elementto provide auxiliary illumination both during initial warmup of thegaseous discharge lamp as lamp as during the cooling off period requiredafter a power interruption of the gaseous discharge lamp.

Still a further object of the invention is to provide an emergencylighting system for gaseous discharge lamps which is relativelyinexpensive and uncomplicated as well as highly efficient.

These and other objects of the present invention will be apparent from areading of the following description and accompanying drawings. Inaccordance with one aspect of the present invention an emergency orauxiliary lighting circuit is provided in conjunction with a gaseousdischarge lamp which includes a single switch means characterized by theabsence of solenoid operated contacts. The switch is biased in anormally closed position. A control circuit is provided for the switchwhich operates in opposition to the bias means. The output voltage ofthe control circuit is proportional to the voltage across the lamp andthus increases as the lamp warms up. As this output voltage reaches apredetermined value, corresponding to the voltage across the gaseousdischarge lame when the lamp reaches the desired output illumination,the control circuit dominates over the biasing means and opens theswitch means, thereby turning off the auxiliary light sourse. Thecontrol circuit senses the high voltage output of the ballast whichoccurs when power is restored after an interruption and the gaseousdischarge lamp is cooling off prior to being restruck by the voltageoutput from the ballast. This insures that the auxiliary light devicewill remain on during the cooling off period until the gaseous dischargelamp is restruck. lmmediately following the restriking of the lamp,however, as the gaseous discharge lamp again warms up to provide thedesired illumination output, the auxiliary lighting circuit will alsoremain on under control of the biasing means.

In a preferred embodiment of the invention the switch means is a reedswitch controlled by an electromagnetic coil and includes a permanentmagnet biasing the reed switch into closed position. The flux from theelectromagnetic coil is fixed to operate in a direction opposite to thatof the magnetic field provided by the permanent magnet.

In a second embodiment the switch is an SCR having its gate positivelybiased and having the voltage across the gaseous discharge lamptransformer coupled, recti tied and inverted to serve as a negativecontrol voltage acting in opposition to the positive bias on the gate. Aunidirectional switch is used as the high voltage sensing device whichoverrides the negative control voltage, thereby permitting the biasingvoltage to hold an SCR in a conducting state until after the striking ofthe arc in the gaseous discharge lamp has occurred.

BRIEF DESCRIPTION OF THE DRAWINGS This invention will be more clearlyunderstood by referring to the drawings wherein similar referencecharacters denote similar elements throughout the views, and in which:

FIG. 1 is a graph illustrating the voltage across the gaseous dischargelamp as a function of time.

FIG. 2 shows the on and off state of the auxiliary lamp device as afunction of time.

FIG. 3 is a schematic diagram illustrating one embodiment of theemergency lighting system in accordance with the present invention.

FIG. 4 is a schematic diagram of an emergency lighting system inaccordance with another embodiment of the present invention.

DESCRIPTION OF THE INVENTION FIG. 1 illustrates a graph of the lampvoltage plotted as a function of time which will be useful inunderstanding the present invention. It is assumed, by way of example,that the circuit contains a gaseous discharge lamp with a ballastproviding voltage there-across with a maximum voltage of approximately250 volts. When the lamp is initially turned on at time T1, the ballastprovides 250 volts to strike an arc in the cold lamp. The ballastprovides its full output voltage at this point which, in turn, ionizesor breaks down the are, causing it to strike. As soon as the arc isstruck the voltage across the lamp drops to approximately 25 volts. Asthe arc heats up between times T1 and T2, there is a relatively lowlight output as the voltage increases across the lamp to approximately85-90 volts at the time T2. At this point there is a minimum acceptablelight output from the lamp. However, the light intensity, as well as thevoltage, continues increasing until time T3 at which time the normaloperating condition for the lamp is reached. At time T3 the voltageacross the lamp is approximately 135 volts with the lamp in a normalfully on condition.

Assume next that a power interruption occurs at time T4. Thisinterruption may result from an opening of the power source by trippingof a circuit breaker due to momentary overloading conditions, etc.Assume further that the power is turned on again at T5 following theinterruption which occurred at T4. Immediately the ballast potentialrises to 250 volts. The lamp however does not light because it is stillin a hot condition and its hot striking potential is higher than 250volts. The unlit lamp therefore begins to cool and after a certainlength of time, until T6, the lamp has cooled sufficiently for the 250volts provided from the ballast to restrike the are. When this occurs,the operation of the lamp repeats similarly to that described for a coldstart wherein the time interval from T6 to T7 reflects the warmup timerequired for the lamp voltage to rise to approximately volts. During thetime interval from T7 to T8, there is minimal desired or acceptablelight output until the normal operating condition for the lamp isreached.

As is evident from the graph of FIG. 1, during the time interval betweenT1 and T2, although the lamp is struck, there is in fact insufficientlight output from the lamp. Furthermore, following a power interruptionsuch as that illustrated during the time interval between T5 to T6, thelamp will remain totally in an off state without providing any light.Thereafter, again, an insufficient illumination will be provided by thislamp between times T6 and T7.

In order to alleviate the problem resulting from the use of gaseousdischarge lamps it would be beneficial and it is within the scope ofthis invention to provide an auxiliary lighting system which is capableof turning on during the time following a power interruption. As isgenerally well known in the art, an incandescent lamp has been typicallyused for auxiliary systems, since such lamps can be turned onimmediately without any delay. It is therefore necessary to provide aswitch for use in conjunction with the incandescent lamp in aconfiguration wherein the switch operates during the required timeperiods. Referring now to FIG. 2, it can be seen that it is necessarythat the switch operate in an on state between times T1 and T2 duringthe warmup time of the gaseous discharge lamp when there is insufficientlight output. Similarly, between times T5 and T6 following powerinterruption the incandescent lamp should remain on and should continuein this on state until time T7 when the gaseous discharge lamp hasreached its minimal acceptable light output and whereupon theincandescent lamp can then turn off.

Referring to FIG. 3, a schematic diagram is shown illustrating oneembodiment of the emergency lighting system in accordance with thepresent invention. The main lighting system includes a gaseous dischargeor are lamp 10 connected to the output terminals of a ballast 12 whichis, in turn, supplied with a source of power from an AC (alternatingcurrent) supply 14. The ballasLneed not be of any special type such as alead or lag type ballast device, but any standard ballast can be used.The voltage across the gaseous discharge is also placed across arectifier 16 which is shown by way of example as a diode bridgerectifier. Capacitor 18 in series with the rectifier l6 acts as avoltage limiting device. While the diode bridge rectifier has beenshown, it is to be understood that other types of devices coming withinthe scope of this invention may be used, such as, for example, atransformer with a pair of appropriately poled diodes in its secondarycircuit.

The output from the rectifier is applied to the electromagnetic coil 20of a reed switch shown generally at 22. Capacitor 24 is connected inparalled relationship with respect to the rectifier output to filter therectifier output.

One contact of the reed switch 22 is connected to the gate electrode oftriac 30. A triac, ,as is well known, is an alternating currentsemiconductor controlled switch having a single control or gateelectrode and a proper signal when applied to the gate causes the triacto conduct current. As long as the signal is present feeding the gate,the triac will remain in a conducting condition. A

resistor 32 is connected in series with the gate of the triac and limitsthe gate current to a safe value.

The auxiliary lamp 34 is connected in series with the triac 30 to oneside of the AC supply. Thus, when the triac is in a conductivecondition, the auxiliary lamp will be turned on. This condition willexist whenever the reed switch is closed.

The reed switch 22, as is well known, usually contains two opposing flatreeds A and 20B of magnetic material which are supported as cantileverswith their free ends overlapping and separated by a small gap.Surrounding the reeds 20A and 20B is the electromagnetic coil 20 soplaced that the magnetic field of the coil encloses the reeds. When thecoil 20 is energised, its magnetic flux pulls the reeds 20A and 20Btogether bringing them into contact and completing thecircuit to thegate of the triac 30. The flux can be in either direction but must be ofsufficient magnitude to cause the reeds to close. As shown in FIG. 3, apermanent magnet 36 is located adjacent to the reed switch structure andprovides a fixed magnetic bias, thereby keeping the reed switch in aclosed condition. Thus, in the presence of low voltage across the arclamp terminals, the reed switch will remain in a closed condition andthe auxiliary lamp will be turned on. The electromagnetic coil 20 is insuch a position, and is connected in such a direction, that the magneticfield produced by it opposes the permanent bias magnet field.

in operation, during the time period from T1 to T2, as the voltage isincreasing across the gaseous discharge lamp, the electromagnetic coil20 is energized and produces a flux opposing the permanent bias magnetfield. However, voltage is low and the resulting electromagnetic fieldis insufficient to overcome the field of the permanent magnet.Therefore, the reeds in the switch remain closed and the auxiliary lampremain, on. At time T2, however, a sufficient voltage is present acrossthe gaseous discharge lamp to cause the coil 20 to produce a field whichbalances the field produced by the permanent bias magnet 36, but whichis in an opposite direction. As a result, there is no net magnetic fieldenclosing the reeds and the contacts of the reed switch 22 open. Fromtime T2 to T3, the voltage continues to increase across thegaseousdischarge lamp and the magnetic field from the electromagnetic coil 20continues to increase in a direction opposite to that of the permanentbias magnet. However, the total net field produced in a single directionacting upon the reed switch contacts is insufficient to cause them toclose. The reed switch therefore remains open and the auxiliary lampremains in an of condition. This phenonenon continues from time T3 to T4wherein the electromagnetic field remains constant but yet sufficient tocause the reed switch to close.

At time, T4, we can assume for purposes of illustration that the poweris interrupted and the electromagnetic field produced by the coil 20will be reduced to zero, permitting the permanent bias magnet to takeover closing the reed switch. However, at T5, if the power is restored,although the gaseous discharge lamp remains off, the ballast voltage isrelatively high (250 volts), and as a result, the field produced by theelectromagnetic coil 20 is high enough to overcome the permanent biasmagnet field and to reclose the reed switch. It is to be remembered thatthe reed switch will close with a flux in either direction. Thus, eventhough the flux in this case is opposite to that of the flux from thepermanent bias magnet, the reed switch responds to a sufficientdifference in the magnetic flux and will close in response thereto. Thereed switch remains closed and the triac conducts current from time T5until time T6 when the gaseous discharge lamp is restruck. At that time,the voltage across the gaseous discharge lamp is suddenly reduced to avery low value (30 volts). The field from the electromagnetic coil 20 istherefore also reduced to a low value. However, at this time the fluxfrom the permanent bias magnet controls and the reed switch will remainclosed under the influence of the permanent bias magnet. As the controlof the switch transfers from the flux in one direction from theelectromagnetic coil to the flux in opposite direction from thepermanent bias magnet, a flicker of the incandescent lamp 34 may occur.The slight flicker however can be reduced by increasing the size of thefilter capacitor 24 thereby increasing its energy storage capability toprevent noticeable flicker of the auxiliary lamp 34. The auxiliary lampremains in its on state until time T7 when the gaseous discharge lamphas sufficient voltage across it to provide acceptable illumination.

Although the circuit has been shown including the triac 30, it is to beunderstood that the triac 30 may be eliminated and the current flowingthrough the reed switch may feed directly to the auxiliary lamp.However, because of the restricted current carried by the reed switch22, this could restrict the voltage of the auxiliary lamp 34. It isnevertheless seen however, that a single switch element, namely the reedswitch 22, can be used to detect both the conditions of high voltage andlow voltage across the gaseous discharge lamp which occur, during itsoperation.

Referring now to FIG. 4, there is shown another embodiment of thisinvention where the gaseous discharge lamp 40 is placed across theoutput of the ballast 42 which is, in turn, energized by an AC source44. Connected to the output of thegaseous discharge lamp 40 is atransformer 46 having a primary 46a and a secondary 46b withappropriately poled diodes 48, 50 connected to the secondary. Ifdesired, a current limiting resistor 47 may be connected in series withthe primary 46a. Although a transformer is shown it is to be understoodthat a rectifier diode bridge may also be used as well as an auxiliarywinding on the ballast to monitor the lamp voltage. The ends of thesecondary of the transformer are interconnected at terminal 52 and theoutput is connected through limiting resistor 54 to one side ofcapacitor 56. The other side of capacitor 56 is connected to a tappedmid-point 58 of the secondary of the transformer 46. Thus, the voltageat point 60 will be negative with respect to the voltage at point, 62. Aresistor 64 is connected to the resistor 54 and to the capacitor 56 tofilter the output from the diodes 48 and 50. The magnitude of thevoltage across the capacitor 56 will be proportional to the voltageacross the gaseous discharge lamp, but will be a negative voltage.

The AC source 44 is also connected across opposite terminals of arectifier containing a diode bridge arrangement 66. The opposite arms ofthe'diode bridge are connected to a series circuit containing a quickstarting auxiliary lamp 68 in series with the anode and cathode of anSCR 70. The gate of the SCR is connected through a resistor 72 to apositive voltage from the diode bridge 66. it is also coupled to thenegative voltage signal from the capacitor 56 through a resistor 74 andan additional capacitor 76. A unidirectional switch 78 is also connectedin parallel across the capacitor 56 and the resistor 64 and receives thenegative voltage therefrom.

As is well known in the art, the unidirectional switch 78 operates suchthat for voltages lower than its breakdown voltage, the switch does notconduct and thus for all practical purposes is not seen by the circuit.When the breakdown voltage of the switch 78 is reached, the device goesinto an avalanche mode of operation and can support only a relativelylow voltage across it. When it is in the avalanche mode of operation,should current through the device drop below a specified holdingcurrent, the device reverts back to its nonconducting state.

In operation, from the time T1 to T2, when the gaseous discharge lamp isin the warmup stage, there is a relatively low voltage across the lamp,Thus, the magnitude ofthe negative voltage feeding the gate of SCR 70will be less than the positive bias-voltage from the resistor 72 and theSCR will be in a conducting state, thereby keeping the auxiliary lamp 68on. As the voltage across the gaseous discharge lamp continues toincrease between time T2 and T3, the magnitude of the negative voltagefeeding the gate of SCR 70 increases greater than the positive bias fromthe resistor 72 and will turn off the SCR 70, thereby extinguishing theauxiliary lamp 68. The auxiliary lamp 68 will remain off be- .tweentimes T3 and T4 or until a power interruption occurs.

At time T4, when the power is momentarily interrupted, the entire systemis in off or a dark state. However, at time T5 when the power isrestored, the gaseous discharge lamp will not restrike immediately, butthere is a very high voltage (approximately 250 volts) across it.Normally, the high voltage should cause the negative voltage feeding thegate of the SCR to be much greater than the positive bias voltage andshould turn the SCR off. Howeventhe voltage from the transformer is nowgreater than the breakdown voltage of the unidirectional switch 78 andcauses it to breakdown and go into its avalanche mode of operationwhereby only a low voltage can be supported across it. Thus, there willonly'be a low negative voltage feeding the gate of the SCR 70 and thepositive bias voltage from resistor 72 will in fact control the SCR.This keeps the SCR in a conducting state and causes auxiliary lamp 68 toremain on.

The various resistors in the circuit are set at specific values toproportionately relate the voltage across the gaseous discharge lamp toappropriate voltages for the various circuit elements such as the SCR 70and the unidirectional switch device 78. It is to be noted, whilegenerally SCR circuits are triggered by a pulse, the present circuitdoes not use a trigger pulse but rather a constant DC bias on the gate.When using a trigger pulse the appropriate timing of the trigger pulseis of critical importance. In the present case, however, such timing isnot necessary since the constant DC bias on the gate no longer makes thetiming a critical factor.

When the auxiliary light is no longer required. the DC bias is simplyremoved and the lamp cxtinguishes.

it is therefore seen that in the present invention a single switchelement is used to detect both the very low voltage during the warmupperiod of the gas discharge lamp to turn the auxiliary lamp on, as wellas the very high voltage after a power interruption to turn theauxiliary lamp on. No electromechanical relays are employed and noadditional parallel circuitry is necessary to shortout or disconnect themain switch element by means of a secondary switching element. Inaddition, no special ballasts are required for operation in connectionwith the circuit. In each case, the single switching element is biasedto keep the suxiliary lamp on and the gaseous discharge lamp voltage isused to provide a voltage opposite to the biasing voltage to turn offthe auxiliary lamp during normal operation of the gaseous dischargelamp.

While the present invention has been described with reference toparticular embodiments thereof. it will be understood that numerousmodifications may be made by those skilled in the art without actuallydeparting from the scope of the invention.

What is claimed is:

1. An auxilairy lighting system for use with a primary lighting systemhaving a gaseous discharge lamp and a ballast connecting the gaseousdischarge lamp to an alternating current source of voltage for ignitingand operating said gaseous discharge lamp, said auxiliary lightingsystem comprising:

a. an auxiliary light source;

b. switch means connected in series with said auxiliary light source andan output from a ballast;

c. said switch means comprising an SCR and a bridge rectifier;

d. biasing means connected in series with said switch means and saidauxiliary light source for producing an output'voltage acting on saidswitch means and maintaining said switch means in a conductivecondition;

c. said biasing means including a resistor connected between a gateelectrode of said SCR and a source of positive voltage; and

f. control means responsive to a voltage across the discharge lamp forproducing an output proportional to said lamp voltage and opposing theoutput voltage of the biasing means;

g. said control means includes a transformer and a rectifier connectedacross a gaseous discharge lamp for producing a negative output voltageproportional to the voltage applied to said discharge lamp;

h. said output voltage from the transformer and rectifier beingconnected to the gate electrode of the SCR;

i. said control means having an output voltage which is greater inmagnitude than said output voltage from the biasing means during aperiod of time when said gaseous discharge lamp is operating at fullillumination and said SCR is in a nonconductive condition, and causingsaid SCR to become conductive in response to application of a startingvoltage to said gaseous discharge lamp;

j. said control means also including a filter circuit and a breakdowndevice connected between the output of the transformer and the rectifierand the gate electrode of the SCR;

k. said breakdown device producing a fixed low voltage after applicationof a high voltage thereto in response to the application of a startingvoltage to the discharge lamp.

2. An auxiliary lighting system as defined in claim 1,

in which:

a. the bridge rectifier is connected to the alternating current sourceof voltage and produces a positive voltage applied at the resistor ofthe biasing means;

3. An auxiliary lighting system as defined in claim 1,

wherein:

a. said transformer has a primary connected across the gaseous dischargelamp and a secondary having ends interconnected at a first terminal;

b. said secondary having an intermediate tap providing a secondterminal;

c. said filter circuit comprising capacitors and resistlamp and to asource of alternating current voltage for igniting and operating saiddischarge lamp;

0. an auxiliary light source; 7

d. rectifier means connected across said gaseous discharge lamp;

c. said rectifier means producing an output;

f. reed switch means comprising an electromagnetic coil enclosing a pairof movable contact elements;

g. said electromagnetic coil being connected to the output from saidrectifier means in parallel with a filter capacitor;

h. said movable contact elements being connected in series with alimiting resistor between an anode and a gate electrode of asemi-conductor switch;

i. said contact elements when closed supplying a voltage to said gateelectrode and causing said semiconductor switch to become conductive;and

j. permanent magnet means positioned adjacent said electromagnetic coiland acting on the movable contact elements to hold the contacts closed;

k. said electromagnetic coil when energized producing a magnetic fieldin opposition to the magnetic field of the permanent magnet;

I. said coil and said permanent magnet having a net field holding thecontacts in engagement after a power interruption and during a warm-upperiod of the lamp;

m. said net field permitting the contacts to separate under conditionswhen the lamp is operating and producing an acceptable level ofillumination. l= l =l l =l= a UNIT D STATES PATENT OFFICE CERTIFICATE OFCORRECTION Patent No. I 3, 87 3; 882 Dated March 25, 1975 Inventor(s) IBernard J. Gershen It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 2, line '35, change -1amp (second instance) to --well--.

Column 5, line 60, change "sufficient" to -'-insufficient--.

Signed and sealed this 20th day of May 1975.

(SEAL) Att St:

e C. MARSHALL DANN RUTH c. MASON Commissioner of Patents AttestingOfficer and Trademarks FORM (9459) USCOMM-DC 60376-P69 U.S. GOVERNMENTPRINTING OFFICE 2 I959 O--3fi6-33l,

1. An auxilairy lighting system for use with a primary lighting system having a gaseous discharge lamp and a ballast connecting the gaseous discharge lamp to an alternating current source of voltage for igniting and operating said gaseous discharge lamp, said auxiliary lighting system comprising: a. an auxiliary light source; b. switch means connected in series with said auxiliary light source and an output from a ballast; c. said switch means comprising an SCR and a bridge rectifier; d. biasing means connected in series with said switch means and said auxiliary light source for producing an output voltage acting on said switch means and maintaining said switch means in a conductive condition; e. said biasing means including a resistor connected between a gate electrode of said SCR and a source of positive voltage; and f. control means responsive to a voltage across the discharge lamp for producing an output proportional to said lamp voltage and opposing the output voltage of the biasing means; g. said control means includes a transformer and a rectifier connected across a gaseous discharge lamp for Producing a negative output voltage proportional to the voltage applied to said discharge lamp; h. said output voltage from the transformer and rectifier being connected to the gate electrode of the SCR; i. said control means having an output voltage which is greater in magnitude than said output voltage from the biasing means during a period of time when said gaseous discharge lamp is operating at full illumination and said SCR is in a nonconductive condition, and causing said SCR to become conductive in response to application of a starting voltage to said gaseous discharge lamp; j. said control means also including a filter circuit and a breakdown device connected between the output of the transformer and the rectifier and the gate electrode of the SCR; k. said breakdown device producing a fixed low voltage after application of a high voltage thereto in response to the application of a starting voltage to the discharge lamp.
 2. An auxiliary lighting system as defined in claim 1, in which: a. the bridge rectifier is connected to the alternating current source of voltage and produces a positive voltage applied at the resistor of the biasing means;
 3. An auxiliary lighting system as defined in claim 1, wherein: a. said transformer has a primary connected across the gaseous discharge lamp and a secondary having ends interconnected at a first terminal; b. said secondary having an intermediate tap providing a second terminal; c. said filter circuit comprising capacitors and resistances connected across said first and second terminals of the transformer secondary.
 4. An auxiliary lighting system as defined in claim 3, wherein: a. said breakdown device comprises a silicon unidirectional switch connected in parallel with one of the filter capacitors.
 5. An auxiliary lighting system as defined in claim 3, which includes: a. a limiting resistor serially connected between the gaseous discharge lamp and the primary of said transformer.
 6. A lighting system, which comprises: a. a gaseous discharge lamp; b. a ballast connnected to said gaseous discharge lamp and to a source of alternating current voltage for igniting and operating said discharge lamp; c. an auxiliary light source; d. rectifier means connected across said gaseous discharge lamp; e. said rectifier means producing an output; f. reed switch means comprising an electromagnetic coil enclosing a pair of movable contact elements; g. said electromagnetic coil being connected to the output from said rectifier means in parallel with a filter capacitor; h. said movable contact elements being connected in series with a limiting resistor between an anode and a gate electrode of a semi-conductor switch; i. said contact elements when closed supplying a voltage to said gate electrode and causing said semi-conductor switch to become conductive; and j. permanent magnet means positioned adjacent said electromagnetic coil and acting on the movable contact elements to hold the contacts closed; k. said electromagnetic coil when energized producing a magnetic field in opposition to the magnetic field of the permanent magnet; l. said coil and said permanent magnet having a net field holding the contacts in engagement after a power interruption and during a warm-up period of the lamp; m. said net field permitting the contacts to separate under conditions when the lamp is operating and producing an acceptable level of illumination. 